1. Field
The present invention relates generally to semiconductor manufacturing and, more particularly, to methods of and apparatus for accessing a process chamber, wherein the access may be optical access through an optical access window, and protection of the optical access window from damage due to conditions originating in the process chamber is facilitated by an improved two-piece configuration of an injector.
2. Description of the Related Art
Vacuum processing chambers have been used for etching materials from substrates and for deposition of materials onto substrates. The substrates have been semiconductor wafers, for example. U.S. Pat. No. 6,230,651 to Ni et al. issued May 15, 2001 (assigned to Lam Research Corporation, the assignee of the present application) is incorporated herein by reference and illustrates an opening, or port, in a dielectric chamber window at a top of a processing chamber to provide access to an interior of the processing chamber, for etching and other processing of semiconductor substrates, for example. For large diameter substrates, center gas injection through the port of the dielectric chamber window was said to ensure uniform etching and deposition, for example, thus improving the access to such processing chambers.
However, as industry standards increased, further improvements were required to provide even better access to such processing chambers. For example, there was a need to monitor the processes in the chambers, which requires chamber access in addition to access for gas supply. When monitoring an optical signal that may indicate a process condition in the process chamber, an opening, referred to as a clear optical aperture, extended through the dielectric chamber window. Such opening, or clear optical aperture, is configured with a straight unobstructed line of sight, thus “clear” is used to describe the optical aperture. Difficulties arose, however, when the clear optical aperture was physically open to the chamber, because plasma may form in the clear optical aperture. Such plasma formation relates to a threshold electric field strength required to initiate a plasma, which threshold strength is based on gas pressure in and the diameter of a bore of the clear optical aperture that is used to supply the gas to the chamber. The Second Prior Application described those two factors of plasma formation in the gas supply bore. Attempts are generally made to reduce this diameter of the gas supply bore, because the gas pressure tends to be specified by process requirements and generally may not be varied for suppressing plasma formation. The Second Prior Application also taught that when there is multiple, or simultaneous, use of the clear optical aperture (i.e., use simultaneously for both optical access and gas supply functions) the multiple use presents conflicting requirements. That is, for the aspect of facilitating monitoring (or diagnosis) of the optical signal that indicates a process condition in the process chamber, there is a need to increase the diameter of the gas supply bore of the clear optical aperture. For example, in providing optical access for interferometric or spectroscopic observation of chamber processes, the diameter of such gas supply bore must generally be not less than a minimum value, which was defined as about one-half inch, for example. This diameter was described as a minimum diameter that is required to enable proper access to the optical signal, and was referred to in the Second Prior Application as the “minimum diameter of the clear optical aperture”. However, the analysis in the Second Prior Application indicated that for the gas supply aspect of the multiple use there was a need for a relatively small diameter (significantly less than 0.5 inch) of the gas supply bore of the clear optical aperture that supplies gas to the chamber, for avoiding plasma formation in the gas supply bore, for example. This analysis also indicated that to facilitate the multiple use, an optical access window must be used to seal the clear optical aperture so as to maintain a vacuum in the processing chamber, and that the optical access window should be mounted at a location at which the strength of the electric field is substantially reduced. Such mounting was to reduce damage to the optical window, e.g., to reduce damage from plasma formation in the clear optical aperture that reduces window clarity. Such plasma may create particulate contamination and promote deposition onto the optical access window. Thus, the analysis in the Second Prior Application indicated that there is not only the minimum diameter of the gas supply bore of the clear optical aperture, which is in conflict with the need for a small diameter gas supply bore, but that there is also a minimum length of such gas supply bores of the clear optical aperture necessary to reduce such contamination and damage to the optical access window that facilitates the multiple use.
In the Second Prior Application this minimum diameter of the clear optical aperture was compared to gas bore passages provided in shielded gas inlets described, for example, in U.S. Pat. No. 6,500,299, issued Dec. 31, 2002 to Mett, et al. Although multiple ones of such passages are provided, the passages are provided only for supplying gas to a process chamber. For such purpose the gas is supplied through grains of dielectric materials such as ceramics, and the passages are defined by interconnected pores of the porous ceramic that do not provide a clear unobstructed line of sight as is required for optical signal transmission. Such passages are thus not suitable for providing clear optical access for the exemplary interferometric or spectroscopic observation of chamber processes. Moreover, it was noted in the Second Prior Application that to mount such passages of a gas bore inside a metal cup and to insert the cup in the side wall of a process chamber as described in the Mett et al. patent, would undesirably subject the metal cup to the plasma in the chamber, for example, and introduce problems in sealing the metal cup to the wall of the process chamber.
The applicants of the present application have determined that as industry requirements or standards have increased beyond those for which the First and Second Prior Applications were directed, and beyond the use of such interconnected pores in ceramic materials for gas supply, further improvements are required to provide even better access to such processing chambers for simultaneous gas supply and optical access through a clear optical aperture, and to do so at less cost for components. For example, the present applicants have identified a need for further improvements that would provide the benefits of the all-ceramic, single piece injector of the Second Prior Application that provided multiple access (i.e., simultaneous gas supply and optical access) to a process chamber, and to have those benefits without the following considerations: (1) requiring the injector to be fabricated from ceramic material, but allowing use of ceramic materials when appropriate, or (2) requiring the injector to be coated with materials such as cerium oxide, zirconium oxide, yttria-stabilized zirconia, thermally-sprayed aluminum oxide, or yttrium oxide deposited on the access aperture protect ceramic materials from the effects of the process plasma, or (3) depositing damaging deposits of particles on an optical access window leading into the injector, or (4) requiring long spacing of an optical access window from the process chamber window to avoid damage to the optical access window, all while facilitating geometric advantages in an improved injector.
In view of the foregoing, the need for methods of and apparatus for providing further improvements in accessing processing chambers includes ways to provide improved multiple access (e.g., simultaneous gas supply and optical access through a clear optical aperture) to a process chamber. This need also includes providing such improved access when the access is for dual zone gas supply, and when the optical access is subject to the conflicting requirements of a relatively large minimum diameter of the clear optical aperture (for optimum optical access) and of a relatively small diameter of a gas bore for gas supply to the chamber, e.g., to avoid plasma formation in the gas bore. The problem presented, then, is how to such provide further improvements in accessing processing chambers, and how to provide such improved access when the access is for dual zone gas supply, and when the optical access is subject to the above conflicting requirements, without the four above considerations.